1. Field of the Invention
The present invention generally relates to printers having fuser units that fuse toner, ink or other printing compositions to a sheet of print media such as a sheet of paper. More particularly, this invention relates to systems for improving the print quality of such printers by adjustment of the operating temperature of their fuser units.
2. Prior Art
It is well known that changes in the operating temperature of a printer""s fuser unit can effect the quality of that printer""s work product. For example, one print quality problem arises from the fact that printers in general, and their fuser units in particular, heat up during extended periods of use. These increasing temperatures can cause changes to those conditions under which a toner or ink best fuses to successive sheets of print media. Thus, increasing fuser temperatures can cause undesired changes in the overall quality of a printing taskxe2x80x94and especially those printing tasks involving a large number of successively printed sheets.
Another print quality problem arises out of the fact that these fusing operations tend to shrink successive sheets of print media, to increasing degrees, as the fuser""s operating temperature rises. In the case of paper print media, these fuser induced sheet size variations are related to the moisture content of successive sheets of paper undergoing printing. For example, it is well known that a sheet of standard 8xc2xdxc3x9711 inch bond paper can shrink as much as an eighth of an inch in either dimension as a result of going through a printer""s fuser unit. A sheet of paper that has absorbed a great deal of the liquid component of an ink, or of a liquid toner, may shrink even more (e.g., up to a quarter of an inch). Those skilled in this art also will appreciate that paper shrinkage in the cross grain direction (normally the width of a sheet of paper) is usually greater than shrinkage in the grain direction (normally the length of a sheet of paper).
Such changes in paper size are generally regarded as being undesirable. They can be especially undesirable in duplex printing operations where a sheet of paper receives printed information within a bordered region on a first side and then undergoes a fusing operation in order to fuse that printed information to that first side. This fusing operation causes the paper to shrink. In a duplex printing operation, that shrunken sheet then undergoes printing on its second side. The information printed on the second side is sized (e.g., in a computer file) in the xe2x80x9cexpectationxe2x80x9d that the print media upon which it is to be placed will be the same size (e.g., 8xc2xdxc3x9711 inches) as the sheet which received the first printing. This expectation may not be met. For example, an original 8xc2xdxc3x9711 inch sheet of paper may have shrunk as much as the previously noted quarter inch in each direction as a result of the fusing operation. In this circumstance, information printed on the second side of the sheet may appear to be larger because the sheet upon which it is printed is, in fact, smaller. Consequently, information appearing on the second side of some kinds of paper also will tend to xe2x80x9cshow throughxe2x80x9d the paper in the border regions of the printing on the first side of that sheet of paper. This condition can create visual effects in the border regions of the first side that vary from reader annoyance, to unprofessional appearance, to commercial unacceptability.
In order to accomplish the toner transfer part of such processes, a sheet of paper must pass between a transfer roller and a photoconductor drum. During the toner transfer, the transfer roller electromagnetically attracts toner particles away from the surface of the photoconductor drum and onto the surface of the sheet of paper. The electrical resistivity of the paper is one of the many factors involved in this toner transfer from the drum to the paper. This electrical resistivity is especially effected by the moisture content of the paper receiving the toner image. This moisture content is, in turn, effected by an electrophotographic printer""s fuser temperature. Thus, in a duplex printing operation carried out by an electrophotographic printer, a fuser temperature change will cause a paper moisture change, which will cause a toner transfer change, which in turn will cause a print quality change.
Those skilled in this art also will appreciate that some printers have dealt with some fuser temperature related problems by allowing manual selection of a fuser temperature. Such selections are usually based upon the nature of the print media to be employed. For example, user selection of a heavy paper print media may call for the printer""s use of a higher fuser temperature mode of operation. This higher temperature provides better print composition adhesion by producing the increased thermal mass transfer needed to sustain adequate fixing of a toner or ink to a heavier grade of paper. In making this selection, a human operator must first recognize that a heavy paper has been selected. That human must then push an appropriate button on the printer""s control panel. If use of the heavier paper is not recognized, or its need for an increased fuser temperature not appreciated, or if the wrong control panel button is pushed, the quality of the printing may suffer.
Another example of a need for selection of a different fuser temperature operating mode might involve printing upon transparent print media since such media are usually best employed using relatively lower fuser temperatures. Such lower temperatures are needed in order to prevent melting or other deformation of the transparent print media itself. Here again, the user must realize that the transparent print media selected requires a lower fuser temperature, and then press the correct button on the printer""s control panel to get that lower temperature.
Thus, under current practices, change of a printer""s fuser temperature requires user recognition of a potential problem arising from the nature of the print media and a correct manual intervention via a front panel interface. Unfortunately, the need for even these relatively simple temperature changes are not intuitive in nature to most users. Moreover, user education is not always an effective way of dealing with this problem since many users do not read the printer""s operating manual, or are otherwise unaware of the print quality problems that can be caused by selection of inappropriate fusing temperatures. Even fewer users are aware that a fuser""s temperature may vary during extended printing operations and/or that these temperature variations can effect the quality of an overall printing task. Thus, many users often interpret poor fusing as a product quality issue. This can result in unneeded service callsxe2x80x94or unjustified user dissatisfaction.
Applicant addresses the previously noted fuser temperature change problems and/or mistaken manual selections at a printer""s control panel by providing those printers that employ fuser units (e.g., electrophotographic printers, inkjet printers and so on) with a fuser temperature control system that automatically changes a fuser""s operating temperature when such a change is needed. Hence, use of printers provided with the hereindescribed self-adjusting fuser temperatures minimize, or entirely eliminate, the need for user knowledge and/or user interaction with a printer""s control panel.
In its broadest sense, the automatic fuser temperature changing printers of this patent disclosure are comprised of (1) a printer, (2) at least two temperature sensors and (3) a printer microprocessor component or separate computer that compares two sensed temperatures and sends signals to a fuser having two or more temperature modes. Applicant""s automatic fuser temperature selection is preferably carried out by (1) a first temperature sensor in a first zone of the printer, (2) a second sensor in a second zone of the printer and (3) a microprocessor or computer for comparing temperatures sensed by the first and second temperature sensors and then making changes in the fuser""s operating temperature based upon a prescribed (e.g., programmed) difference between the two temperatures. Thus, based upon a predetermined (and programmed) temperature difference (or xe2x80x9cdeltaxe2x80x9d) existing between the two zones, the microprocessor or computer will send a signal to a fuser temperature control device that will change the fuser to a mode of operation employing a different temperature. If the temperature difference is xe2x80x9cnot large enoughxe2x80x9d, the microprocessor or computer will not send a temperature change signal to the fuser""s temperature control device.
Preferably, the fuser units used in applicant""s printers will have several operating temperature modes (e.g., from two to about ten such modes are preferred; three modes xe2x80x9cLowxe2x80x9d, xe2x80x9cMediumxe2x80x9d and xe2x80x9cHighxe2x80x9d are even more preferred). Changes between these fuser temperature operating modes can be made based upon attainment of certain prescribed temperature differentials between the first zone and the second zone. Thus, such a microprocessor will first detect a temperature differential between a first sensor in a first zone of the printer and a second sensor in a second zone of that printer. The printer""s microprocessor or computer would then (in conjunction with a predetermined computer program) determine whether or not that temperature differential is great enough to warrant changing the fuser to a different operating temperature mode.
In some of the more preferred embodiments of this invention, the fuser temperature selections are made based upon sensing a temperature differences between two zones that are located entirely within the housing of the printer. In some of the most preferred embodiments of this invention, the first such zone will lie between a sheet input side of the printer and its print mechanism (e.g., an electrophotographic printer""s toner transfer mechanism, an inkjet printer""s inkjet nozzles, etc.). Such a first zone also may be referred to as a xe2x80x9cmedia input zonexe2x80x9d in this patent disclosure. The second zone will lie between the fuser unit and a sheet exit side of the printer. This second zone may be hereinafter referred to as a xe2x80x9cmedia output zonexe2x80x9d. Thus, if the temperature difference between the media input zone and the media output zone is not large enough, the microprocessor would assume that the fuser""s temperature is not appropriate and it would select a new fuser temperature based upon the dictates of a computer program.
The underlying apparatus and principles of the present patent disclosure can be applied to any printer that employs a fuser unit (e.g., electrophotographic printers, inkjet printers, etc.). Consequently, those skilled in this art will appreciate that, for purposes of this patent disclosure, a xe2x80x9cfirstxe2x80x9d or a xe2x80x9cmedia input zonexe2x80x9d that includes a toner transfer unit is analogous to a xe2x80x9cfirstxe2x80x9d or xe2x80x9cmedia input zonexe2x80x9d that includes an inkjet print head. They are analogous because applicant""s invention is primarily concerned with detecting a temperature in these zones rather than being concerned with the nature of the printing operations carried out in them. Similarly, applicant""s invention is primarily concerned with detecting a temperature in a xe2x80x9csecondxe2x80x9d or xe2x80x9cmedia output zonexe2x80x9d rather than with the mechanical operations carried in that second zone. Hence, the hereindescribed fuser temperature control systems can be used in inkjet printers, electrophotographic printers or any other printer that employs a fuser unit. Electrophotographic printers are, however, particularly well suited to the use of the hereindisclosed fuser temperature adjustment devices. Hence, application of the present invention to an electrophotographic printer will be emphasized to illustrate this invention.
Applicant""s fuser units are preferably comprised of two opposing rollers that roll over each other in heated, pressured, rolling contact. In some of the more preferred embodiments of this invention, at least one of the two opposing rollers will contain a heating device that is heated by electrical power delivered to an inductive heater element or to a halogen tube. Other fusers may be in the form of a heated plate over which, or under which, a printed sheet passes. In either case, an appropriate signal from a printer""s microprocessor to its fuser controller unit will cause that fuser controller unit to provide more (or less) power to such an inductive heater element or halogen tube and thereby change the fuser""s operating temperature. Use of two opposing rollers wherein each of the two opposing rollers contains a heating device is also contemplated in the practice of this invention. Use of a powered heater roller also is contemplated. Use of two separately powered rollers also is possible, but not preferred. Moreover, one or both of the rollers may have a mechanism for adjusting the position of the rollers"" axlexe2x80x94and hence adjusting the operating pressure of that roller with respect to the opposing roller, and hence with respect to a sheet of print media passing between the two rollers. Similarly, the rotational speed of a drive roller""s axle may be increased or decreased to provide shorter or longer sheet residence times in the fuser unit.
The temperature and pressure conditions existing in the roller type fuser units of this patent disclosure (e.g., the fuser unit 46/48 shown in FIG. 2) can vary considerably. They can vary with respect to each other and they can vary with respect to the residence time of a sheet of print media (e.g., paper) passing through such a fuser unit. Generally speaking, these temperatures will vary between about 85xc2x0 C. and about 96xc2x0 C. Temperatures between about 87 and 91xc2x0 C. are however somewhat preferred in those cases where polymer based toner particles are applied to a paper feedstock by an electrophotographic printer. The pressure conditions experienced by a sheet of media in applicant""s fuser units will generally range between about 5 and about 8 psi. Pressures ranging between about 6 and about 7 psi are preferred, especially when the fuser unit""s operating temperature is between about 87xc2x0 C. and about 91xc2x0 C. and the print media is paper.
The residence time of a sheet of print media in a such fuser unit will usually be determined by the angular velocity of a powered drive roller component of such a fuser (e.g., pressure roller 46 of FIG. 2). Typical residence times for 8xc2xdxc3x9711 inch sheets of paper generally will be from about 2 to about 8 seconds per sheet. Residence times of about 3 to about 6 seconds are somewhat more preferred. Thus, these preferred residence times generally correspond to 8xc2xdxc3x9711 inch paper processing rates of about 16 to about 32 sheets per minute. Generally speaking, shorter residence times will be used as the operating temperature is raised. For example, the lower end of the residence time range (e.g., 2-3 seconds) will generally be preferred as the temperature is raised toward the upper regions of its operating temperature range (e.g., between about 91xc2x0 C. and about 93xc2x0 C.).
Some of the more preferred embodiments of this invention will involve printers (electrophotographic printers, inkjet printers or other fuser-containing printers) wherein: (1) a first temperature sensor senses an ambient temperature in a first zone, (2) a first temperature sensor senses the temperature of a sheet of print media in a first zone, (3) a second temperature sensor senses an ambient temperature in a second zone, (4) a second temperature sensor senses the temperature of a sheet of print media in a second zone, (5) a first zone is located between the sheet input side of the printer and a point on a media path through the printer that is prior to the fuser unit, (6) a first zone is located between the sheet input side of an electrophotographic printer and a point on a media path through that printer that is prior to its toner transfer mechanism, (7) a first zone is located between a sheet input side of an inkjet printer and a point on the media path that is prior to its inkjet printer head, (8) a second zone is located between the sheet output side of a printer and a point on the media path through the printer that is just after the toner fuser unit, (9) a microprocessor unit of the printer or a separate and distinct computer unit send electrical signals to a fuser control unit in order to change the fuser unit""s operating temperature and its operating pressure, (10) a microprocessor unit of the printer or a separate and distinct computer unit sends electrical signals to a fuser control unit in order to change the fuser unit""s operating temperature and its operating speed, (11) a microprocessor unit of the printer or a separate and distinct computer unit sends electrical signals to a fuser control unit in order to change the fuser unit""s operating temperature, pressure and speed, (12) a fuser unit has two opposing rollers and wherein at least one of the two opposing rollers contains a heating device employing an inductive heater element, (13) a fuser unit has two opposing rollers and wherein at least one of the two opposing rollers contains a heating device employing a halogen tube, (14) a fuser unit has two opposing rollers and wherein each of the two opposing rollers contains a heating device, (15) a fuser unit has an operating speed such that a sheet of 8xc2xdxc3x9711 inch paper passing through said fuser unit has a residence time therein of from about 2 to about 8 seconds, (16) a fuser unit has an operating speed such that a sheet of 8xc2xdxc3x9711 inch paper passing through said fuser unit has a residence time therein of from about 2 to about 3 seconds and (17) a fuser unit is a heated plate that does not contact a printed sheet as said sheet passes over or under said heated plate.